fix(spark_generator): improve method body extraction for components

- Correctly skip method parameter lists (including named parameters and default values) to prevent premature body detection.
- Make getMethodSource visible for testing and add comprehensive unit tests for various method signatures (named parameters, nested braces, arrow functions).
- Bump version to 1.0.0-alpha.15 and update CHANGELOG.

Author: kevin-sakemaer

packages/spark_generator/pubspec.yaml

@@ -11,6 +11,7 @@ environment:
   sdk: ^3.10.0
 
 dependencies:
+  meta: ^1.11.0
   build: ^4.0.4
   source_gen: ^4.1.2
   analyzer: ^10.0.1